Breeding occurs sometime in February or March at lower elevations, but does not occur until March or April at the two Washington sites in the Cascade Range (McAllister and Leonard 1997). The Oregon Spotted Frog exhibits strong fidelity to breeding sites and eggs are often deposited the same locations in successive years.
Males arrive first, gathering in "lek-like" groups and float in the shallows, calling while awaiting the arrival of a female. Male advertisement calls, consisting of a rapid series of 5 to 50 faint "tapping" notes notes, are given throughout the breeding season (particularly on sunny days) and again in fall (Davidson 1995; Leonard et al. 1997). Most breeding takes place within a two-to-three-week "window" when most of eggs are deposited. However, breeding may be interrupted for up to several weeks by the onset of cold weather; in such cases a second bout of breeding may occur. Upon release, the ova are tightly packed in a mass roughly the size of a ping-pong ball, but within a few hours the mass swells to the size of an average-size human fist. Females usually lay their eggs atop or adjacent to other egg masses (some of the larger aggregations may contain more than 100 individual egg masses). The egg masses are not attached to vegetation, but are deposited in still, shallow waters atop submergent herbaceous vegetation or freely floating amongst clumps of emergent wetland plants such as sedges (Carex spp.) and rushes (Juncus spp). Often-times, the the upper portions of the egg masses protrude above the water surface resulting in severe egg mortality from freeze-thaw damage or desiccation.
After a few weeks of embryonic development, thousands of small tadpoles emerge and cling to the remnants of the gelatinous egg masses, their densely packed, dark bodies acting as solar collectors and warming the water adjacent to the mass. After several days, the hatchlings become free-swimming tadpoles, using their minute brush-like mouthparts to feed upon algae, detritus, and, in some cases, bacteria (but see McDiarmid and Altig 1999). Tadpoles may grow to 90 mm total length before metamorphosing in their first summer or fall (Licht 1975) .
Mortality of eggs, tadpoles, and newly metamorphosed frogs is high, and it is likely that only about 1% of an annual cohort survive to the first winter (Licht 1974) . Near sea-level sexual maturity is attained at age two, while at higher elevations one or two additional years is required (Licht 1975).
Adults feed upon arthropods (e.g., spiders, insects), earthworms and other invertebrate prey. In turn, Oregon Spotted Frogs may be preyed upon by mink, river otter, raccoon, herons, bitterns, corvids and garter snakes (Licht 1974) , while larvae may be consumed by larvae of dragonflies, predacious diving beetles, fish, garter snakes and wading birds.